The present invention relates to a portable radio apparatus, and in particular, to a portable radio apparatus which can be folded.
Description of the Related Art
Heretofore, as a portable and foldable telephone, there has been known a portable telephone constituted with a first casing including an earpiece speaker and a second casing including a mouthpiece microphone in which the first casing is linked with the second casing by a hinge, thereby enabling the telephone to be folded and to be unfolded for use.
In general, the portable telephone sets are operated with radio frequencies ranging from several hundred of megahertz to several gigahertz. For each portable telephone, the wavelength of a radio wave used is set to a value similar to a length of a longer side of a casing thereof.
As for an antenna, in general, when a grounding plate thereof supporting a main portion thereof has a large area, characteristics of the antenna are not substantially influenced by a shape of the grounding plate. However, when the size of the plate becomes similar to the wavelength of radio wave used for transmission and reception, the characteristics are considerably influenced by the contour thereof. According to usual designs of a portable telephone, the casing thereof also functions as the grounding plate and hence the characteristics of the antenna are remarkably influenced by the shape of the telephone casing. In consequence, the matching of the antenna with respect to the transmission and reception is established in accordance with the final contour of the casing of the portable telephone.
As above, the final contour of the casing exerts a great influence upon the matching of the antenna in operation. In this connection, however, the shape of the portable and foldable telephone considerably varies between the unfolded and folded states with respect to the antenna characteristics. In more detail, the longitudinal size of the casing in the unfolded state is about twice that of the casing in the folded state.
However, in accordance with the designs of the conventional portable radio apparatus, the matching of the antenna is to be established only when the casing is unfolded with transmitting and receiving circuits. This consequently leads to a problem that the folded telephone in a call waiting state cannot obtain the inherent effective receiving sensitivity.
On the other hand, when the antenna matching is established when the apparatus is in the folded state, there arises a problem, although the effective receiving sensitivity is increased in the call waiting state, that the effective receiving sensitivity and the effective transmitting radiation power are decreased in the operating, i. e., unfolded state.